Mechanical and chemical-mechanical planarizing processes (collectively “CMP”) remove material from the surface of semiconductor wafers, field emission displays, read/write heads or other microelectronic workpieces in the production of microelectronic devices and other products. FIG. 1 schematically illustrates a CMP machine 10 with a platen 20, a carrier assembly 30, and a planarizing pad 40. The CMP machine 10 may also have an under-pad 25 attached to an upper surface 22 of the platen 20 and the lower surface of the planarizing pad 40. A drive assembly 26 rotates the platen 20 (indicated by arrow F), or it reciprocates the platen 20 back and forth (indicated by arrow G). Since the planarizing pad 40 is attached to the under-pad 25, the planarizing pad 40 moves with the platen 20 during planarization.
The carrier assembly 30 has a head 32 to which a workpiece 12 may be attached, or the workpiece 12 may be attached to a resilient pad 34 in the head 32. The head 32 may be a free-floating wafer carrier, or an actuator assembly 36 may be coupled to the head 32 to impart axial and/or rotational motion to the workpiece 12 (indicated by arrows H and I, respectively).
The planarizing pad 40 and a planarizing solution 44 on the pad 40 collectively define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the workpiece 12. The planarizing pad 40 can be a soft pad or a hard pad. The planarizing pad 40 can also be a fixed-abrasive planarizing pad in which abrasive particles are fixedly bonded to a suspension material. In fixed-abrasive applications, the planarizing solution 44 is typically a non-abrasive “clean solution” without abrasive particles. In other applications, the planarizing pad 40 can be a non-abrasive pad composed of a polymeric material (e.g., polyurethane), resin, felt or other suitable materials. The planarizing solutions 44 used with the non-abrasive planarizing pads are typically abrasive slurries with abrasive particles suspended in a liquid.
To planarize the workpiece 12 with the CMP machine 10, the carrier assembly 30 presses the workpiece 12 face-downward against the polishing medium. More specifically, the carrier assembly 30 generally presses the workpiece 12 against the planarizing liquid 44 on a planarizing surface 42 of the planarizing pad 40, and the platen 20 and/or the carrier assembly 30 move to rub the workpiece 12 against the planarizing surface 42. As the workpiece 12 rubs against the planarizing surface 42, material is removed from the face of the workpiece 12.
CMP processes should consistently and accurately produce a uniformly planar surface on the workpiece to enable precise fabrication of circuits and photo-patterns. During the construction of transistors, contacts, interconnects and other features, many workpieces develop large “step heights” that create highly topographic surfaces. Such highly topographical surfaces can impair the accuracy of subsequent photolithographic procedures and other processes that are necessary for forming sub-micron features. For example, it is difficult to accurately focus photo patterns to within tolerances approaching 0.1 micron on topographic surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical surface into a highly uniform, planar surface at various stages of manufacturing microelectronic devices on a workpiece.
In the highly competitive semiconductor industry, it is also desirable to maximize the throughput of CMP processing by producing a planar surface on a workpiece as quickly as possible. The throughput of CMP processing is a function, at least in part, of the polishing rate of the planarizing cycle and the ability to accurately stop CMP processing at a desired endpoint. Therefore, it is generally desirable for CMP processes to provide (a) a desired polishing rate gradient across the face of a substrate to enhance the planarity of the finished surface, and (b) a reasonably consistent polishing rate during a planarizing cycle to enhance the accuracy of determining the endpoint of a planarizing cycle.
Conventional planarizing machines may not provide consistent polishing rates because of nonuniformities in (a) the distribution of the slurry across the processing pad, (b) the wear of the processing pad, and/or (c) the temperature of the processing pad. The distribution of the planarizing solution across the surface of the processing pad may not be uniform because conventional planarizing machines typically discharge the planarizing solution onto a single point at the center of the pad. This causes a thicker layer of planarizing solution to be at the center of the pad than at the perimeter, which may result in different polishing rates across the pad. Additionally, the nonuniform distribution of the planarizing solution may cause the center region of the pad to behave differently than the perimeter region because many low PH solutions used during planarizing cycles are similar to cleaning solutions for removing stains and waste matter from the pads when polishing metallic surfaces. Such low PH planarizing solutions dispersed locally accordingly may change the physical characteristics differently at the center of the pad than at the perimeter. The nonuniform distribution of planarizing solution also causes a nonuniform temperature distribution across the pad because the planarizing solution is typically at a different temperature than the processing pads. For example, when the planarizing solution is at a lower temperature than the pad, the temperature near the single dispensing point of the planarizing solution is typically lower than other areas of the processing pad.
One concern of manufacturing microelectronic workpieces is that the distribution of the planarizing solution can cause variances in the planarized surface of the workpieces. For example, an inconsistent distribution of planarizing solution between the workpiece and the pad can cause certain areas of the workpiece to planarize faster than other areas. Nonuniform pad wear and nonuniform temperature distributions across the processing pad can also cause inconsistent planarizing results that (a) reduce the planarity and uniformity of the planarized surface on the workpieces, and (b) reduce the accuracy of endpointing the planarizing cycles. Therefore, it would be desirable to develop more consistent planarizing procedures and machines to provide more accurate planarization of microelectronic workpieces.